Apparatus for the detection of pattern edges

Abstract

Apparatus for detecting the edge of a pattern on an object surface is disclosed. The apparatus includes a light source for emitting a collimated light beam, a condensing optical system for forming an elongated light spot of the collimated light beam on the object surface, an image-forming optical system for forming an image of the elongated light spot by focusing the reflected light from the object surface, a detector for forming an output signal corresponding to the reflected light from the spot image, an image rotator and a driving member. The elongated light spot is formed by means of slit. The direction of the slit is changed by the driving member to change the direction of the elongated light spot on the object surface. The driving member also drives the image rotator so as to keep the direction of the reflected spot image unchanged irrespective of the change of the direction of the slit.

I claim: 
     
       1. Apparatus for detecting the edge of a pattern on an object surface, comprising: light source means for emitting a collimated light beam;   a slit screen member having at least one slit for allowing light to pass therethrough and disposed in said collimated light beam;   a condensing optical system for focusing the collimated light beam passed through said slit on the object surface to form a light spot on the object surface which is elongated in a direction determined by the direction of said slit;   signal forming means including an image-forming optical system for focusing reflected light from the object surface illuminated by the light spot to form an image of said elongated light spot, said signal forming means forming an output signal corresponding to said light spot image;   image rotating means disposed in the optical path of said reflected light passing through the image-forming optical system; and   driving means for changing the direction of the slit to change the direction of the elongated light spot on the object surface and driving said image rotating mean in accordance with the change of the direction of the slit so as to keep the light spot image formed by the image-forming optical system unchanged in direction.   
     
     
       2. Apparatus according to claim 1, wherein said image rotating means includes an image rotator mounted for rotation about a rotation axis parallel with the optical path of said reflected light to rotate light exiting from said image rotator relative to light incident on said image rotator about the rotation axis in accordance with the rotation of said image rotator. 
     
     
       3. Apparatus according to claim 1, which further comprises means for detecting scattered light generated at the edge of the pattern on the object surface when the pattern edge is illuminated by said light spot. 
     
     
       4. Apparatus according to claim 3, wherein said scattered light detecting means includes a sensor for forming a photoelectric output corresponding to detected scattered light and wherein said output signal is used to set the light detection sensitivity of said sensor. 
     
     
       5. Apparatus according to claim 1, wherein said slit screen member comprises a screen disk having plural slits formed therein and rotatable in a plane intersecting the collimated light beam, said slits being distributed in different positions in the disk and extending in different directions relative to the radial direction of the disk. 
     
     
       6. Apparatus according to claim 5, wherein said disk has plural rotational angular positions to each of which said disk can be rotated by said driving means to bring a corresponding one of said slits into the collimated light beam. 
     
     
       7. Apparatus according to claim 6, wherein every slit in the disk is so formed that said corresponding one in the collimated light beam is at a position deviated from the optical axis of the condensing optical system. 
     
     
       8. Apparatus according to claim 1, wherein said light source means and said condensing optical system have a common optical axis and said slit screen member has a rotation axis aligned with the common optical axis and wherein said at least one slit is provided in the vicinity of the rotation axis. 
     
     
       9. Apparatus according to claim 1, wherein said image-forming optical system focuses light reflected by the object surface and collimated through the condensing optical system. 
     
     
       10. Apparatus according to claim 9, wherein said image-forming optical system includes an inverted beam expander for reducing the beam diameter of said reflected, collimated light and a focusing member for focusing the beam diameter-reduced light. 
     
     
       11. Apparatus according to claim 10, wherein said image rotating means is disposed between the inverted beam expander and the focusing member. 
     
     
       12. Apparatus according to claim 9, wherein said image-forming optical system includes a polarized beam splitter disposed between the slit screen member and the condensing optical system and a quarter wavelength member disposed between the polarized beam splitter and the condensing optical system. 
     
     
       13. Apparatus for detecting the edge of a pattern on an object surface, comprising: light source means for emitting a collimated light beam;   a condensing optical system for focusing the collimated light beam on the object surface to form a light spot on the object surface;   an optical means disposed in the collimated light beam for processing said beam in such manner that the light spot has an illumination area in a determined direction on the object surface;   signal forming means including an image-forming optical system for focusing reflected light from the object surface illuminated by the light spot to form an image of said light spot, said signal forming means forming an output signal corresponding to said light spot image;   image rotating means disposed in the optical path of said reflected light passing through the image-forming optical system; and   driving means for operating said optical means to change the direction of said illumination area of the light spot on the object surface and driving said image rotating means in accordance with the operation of said optical means so as to keep the light spot image formed by the image-forming optical system unchanged in direction.